1. Field of the Invention
The present invention relates to a pumped storage power plant.
2. Description of the Related Art
In a conventional pumped storage power plant, a power generation operation and a pumping operation are carried out by utilizing a difference in a geographical water level between two regulating reservoirs (an upper regulating reservoir and a lower regulating reservoir) whose water surfaces are open to the atmosphere. In some cases, one of the regulating reservoirs is underground. Even in this case, the underground regulating reservoir is configured such that the water surface thereof is open to the atmosphere in the underground space.
In the pumping operation, the pumped storage power plant pumps up water in the lower regulating reservoir to the upper regulating reservoir to convert an electrical energy as a pumping input into a potential energy of the water and thereby store the energy. Here, an electrical energy consumed by pumping up the water in the pumping operation is determined depending on a characteristic of a pump turbine used in the pumped storage power plant and a water level difference between the water level of the upper regulating reservoir and the water level of the lower regulating reservoir.
A conventional pumped storage power plant is disclosed in the following Non-Patent Literature 1: Turel, V., F. Prime, and T. Machino, “Implementation of a Variable Speed Unit in the AVCE PSPP”, Hydro 2008.
According to the above-mentioned conventional technique, an electrical energy used for pumping up the water in the pumping operation is input as the pumping input from an external grid. A desired water level difference between the water level of the upper regulating reservoir and the water level of the lower regulating reservoir required for consuming the pumping input can be determined by the characteristic of the pump turbine. However, an actual water level difference between the water level of the upper regulating reservoir and the water level of the lower regulating reservoir cannot be adjusted to the desired water level difference. Moreover, the pumping input that is input from the external grid is not necessarily constant but may change. Therefore, the pumping input may not be stably consumed in the pumping operation.